Recently released political ads reveal the Republican Party’s two-pronged election strategy: one message for skeptics and swing voters, and a very different one aimed at President Trump’s base.Published OnNov. 1, 2018CreditCreditSarah Silbiger/The New York Times

Immigration has been the animating issue of the Trump presidency, and now — with the possibility that Republicans could face significant losses in the midterm elections on Tuesday — the president has fully embraced a dark, anti-immigrant message in the hope that stoking fear will motivate voters to reject Democrats.

In a rambling speech on Thursday afternoon that was riddled with falsehoods and vague promises to confront a “crisis” at the border, Mr. Trump used the official backdrop of the White House to step up his efforts to demonize a caravan of Central Americans that has been making its way through Mexico, assail Democrats, and promote a vision of a United States that would be better off with fewer immigrants.

The president said he had ordered troops to respond to any migrants in the caravan who throw rocks as if they were brandishing firearms, saying, “I told them: Consider it a rifle.” He said his government had already begun to construct “massive cities of tents” to imprison legal and illegal immigrants who try to enter the United States.

“This is a defense of our country,” Mr. Trump declared from a lectern in the Roosevelt Room before leaving the White House to attend a campaign rally in Missouri. “We have no choice. We will defend our borders. We will defend our country.”

The president also played fast and loose with the truth. At one point, he said that 97 percent of immigrants apprehended at the border and released into the United States do not show up for their trials; the number is closer to 28 percent. He also said the government is no longer releasing immigrants while they await trial. Meanwhile, migrants are being caught and released at the border regularly, as has happened for decades.

He repeated his oft-stated, misleading description of the situation south of the border, saying that “large, organized caravans” are heading toward the United States, filled with “tough people, in many cases.”

“A lot of young men, strong men,” he continued, “and a lot of men we maybe don’t want in our country.”

“They have injured; they have attacked,” he added.

In recent weeks, Mr. Trump has promised a number of actions to demonstrate a renewed crackdown on immigrants. While he has followed through on one of them — ordering an increase in military units on the border — there was no mention in the speech of the presidential proclamation on asylum and the new policy on family separation that he has promised.

Image

Part of a migrant caravan heading through Mexico. Before the midterms, Mr. Trump is making immigrants his singular focus.CreditGuillermo Arias/Agence France-Presse — Getty Images

Mostly what the president offered was a repeat of the angry rhetoric that has been a central theme of his campaign rallies and in Fox News interviews for the past two weeks.

A new proposal to give migrant families the choice to willingly separate from their children? “We are working” on it, Mr. Trump said. The presidential proclamation and regulation aides had promised to bring an end to asylum for illegal immigrants? They are “finalizing” them, he added. He promised an executive order next week, providing no details but saying it would be “quite comprehensive.”

Raising fears about immigrants has been a central theme for Mr. Trump since he first announced he was running for president. On Thursday night, in a chilly airplane hangar in Columbia, Mo., with Air Force One as his backdrop, Mr. Trump whipped thousands of supporters into a chorus of boos over the constitutional guarantee of birthright citizenship, dismissing a core tenet of the 14th Amendment as a “crazy, lunatic policy that we can end.”

He warned that the Constitution’s grant of citizenship to any person born on United States soil could benefit the offspring of “an enemy of our country” or “a dictator with war on your mind.”

“Democrats want to spend your money and give away your resources for the benefit of anyone but American citizens,” he charged falsely, crystallizing his fear-mongering closing message: “If you don’t want America to be overrun by masses of illegal immigrants and massive caravans, you better vote Republican.”

In the past week, as a series of pipe bombs sent to prominent opponents of the president and then the killing of 11 people at a Pittsburgh synagogue dominated the news, the president’s political team has urged him to put renewed emphasis on immigration and use his bully pulpit to ratchet up the nation’s sense of alarm about the dangers of migrants heading for the border.

The president did not need much convincing. On Wednesday afternoon, he tweeted out a 53-second, expletive-filled video that features immigrants charged with violent crimes and images of a throng of brown-skinned men breaching a barrier and running forward. The president’s message was clear: Immigrants will kill you, and the Democrats are to blame.

“It is outrageous what the Democrats are doing to our Country,” Mr. Trump wrote in thetweet, part of a grim warning about the dangers of immigrants that has left some Republicans — including the House speaker, Paul D. Ryan — uneasy heading into Tuesday’s voting.

Still, the president’s dark rhetoric has clearly put some Democratic candidates on the defensive, especially in conservative states where Mr. Trump won by wide margins in 2016. In the last several days, Senator Claire McCaskill, Democrat of Missouri, has embraced some of the president’s anti-immigrant messaging as she fights for re-election, telling Fox News that “I do not want our borders overrun, and I support the president’s efforts to make sure they’re not.”

In his remarks on Thursday afternoon, Mr. Trump appeared to promise a lethal response from the military if migrants threw rocks at soldiers. At Northern Command, the military headquarters overseeing the newly announced deployments to the border, military officials were shocked upon hearing the president’s comments.

A Defense Department official said the American military’s rules of engagement allowed deadly force to be used if a service member was faced with an imminent threat of death or injury. But the official said the military units headed to the border with weapons, such as the military police, would keep them stored unless told otherwise. The official could not say if they would be issued ammunition, but did not expect them to be in a position to use their weapons.

But the president dismissed questions about whether all of his ideas would be legal under American law.

“Oh, this is totally legal,” he said. “No. This is legal.”

Others say that it would depend on the details of Mr. Trump’s proposals, which have not been disclosed. If Mr. Trump moves to deny asylum to all undocumented immigrants, for example, that would be illegal, according to Stephen Legomsky, a Washington University School of Law professor and former chief counsel for U.S. Citizenship and Immigration Services.

“Such a policy would be in clear violation of the U.S. asylum laws and an equally clear violation of our international treaty obligations,” he said. “Once a person enters our territory, there is no analogous law that permits a blanket denial of asylum.”

But details aside, Mr. Trump is betting that a relentless focus on the threat he envisions from immigrants crossing the Mexican border, combined with his repeated assertion that Democrats are to blame for letting them into the country, will energize conservative supporters. And he is hoping that the dark imagery will not alienate suburban voters — especially women — who have already been abandoning Republicans in droves.

It is a risky bet. Last year, the Republican candidate for governor in Virginia lost after running dark ads warning of the dangers of marauding MS-13 gangs in the state. And the president’s determined effort to shift the conversation away from issues like low unemployment, tax cuts, conservative Supreme Court justices and reduced regulation has worried many Republicans.

At the beginning of the week, Mr. Trump’s campaign put out a 60-second television ad appealing to the message those Republicans have advocated. It featured a suburban woman who frets about the possibility that the economic recovery could be fleeting. But the president’s comments about the dangers of the Central American caravan and his new ad about violent immigrants attracted far more attention.

The immigration video, which relies solely on news clips and stock footage, includes courtroom footage of Luis Bracamontes, a twice-deported Mexican immigrant sentenced to death this year for killing two California law enforcement officers.

Two people close to Mr. Trump declined to say whether it was made by the White House video unit or someone on the campaign. But one White House official, who was not authorized to speak publicly, said that it had been in the works for several days, and was released on Wednesday in an effort to change the focus of cable television from the pipe bombs and the Pittsburgh killings.

At his rally on Thursday, the president hinted that the effort to change the subject had worked.

Mr. Trump, who is in the middle of an 11-rally sprint across the country, lamented that the rash of pipe bombs targeting his political opponents and the synagogue massacre last weekend had diverted attention from his push to elect Republicans.

“For seven days, nobody talked about the election — it stopped the tremendous momentum,” he said, adding that “now, the momentum is picking up.”